What is catalyst reaction

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catalysis

In addition to concentration and temperature, the rate of reaction in a system is determined by the presence of catalysts. Influencing the reaction rate is known as catalysis. A distinction is made here:

  • homogeneous catalysis: the catalyst is in one phase with the reacting substances (solution or gas phase).
  • heterogeneous catalysis: the catalyst forms its own (mostly solid) phase.

In the past, a distinction was occasionally made between positive and negative catalysis. Positive catalysis corresponds to the usual case of an increase in the reaction rate by the catalyst. The less common term negative catalysis is actually to be understood as a deactivation, i.e. a reduction in the reaction rate, for example by intercepting or complexing catalytically active substances.

As different as the mode of action of the catalysts, i.e. the reaction mechanism of catalyzed reactions, can be, some common basic principles can be named:

Note
A catalyst only influences the reaction rate of the equilibrium establishment, not the position of the equilibrium of a reaction. It leaves the initial and final state of the reaction unchanged and therefore cannot trigger a thermodynamically impossible reaction. A catalyst influences the forward and backward reactions equally.

There is no single theory of catalysis, rather there are different models for certain classes of catalytic reactions. Catalytic effects are always caused by intensive interactions between the reactants and the catalyst. This can lead to the formation of chemical bonds between the reacting molecules and the catalyst; this intermediate product then reacts further to form the end products, the catalyst being released again, that is, the catalyst is only required in relatively low concentrations and not in stoichiometric amounts. A catalyzed reaction can be formulated as

The alternative representation focuses on the changes to the catalytic converter.

On the other hand, the catalytic effect can also be of a more physical nature, for example in such a way that the electron bonds are loosened through polarization and the reaction partner then reacts more easily.

In any case, the catalyst changes the mechanism of the reaction in question. It is crucial here that the catalyzed reaction proceeds with a lower activation energy than the uncatalyzed one, which in turn leads to an increase in the reaction rate.